This invention relates generally to the controls for an air conditioning system and more particularly to an improved installation which facilitates servicing and adjustment of the control components for a variable volume air diffuser.
U.S. Pat. Nos. 4,399,739 to Dean; 4,356,963 to Edwards et al., 4,331,291 to Dean and 4,312,475 to Edwards et al. relate to variable volume air distribution systems in which operating power for the flow control mechanism is obtained from the high pressure air supply in the ventilating ducts of a building. As described in the aforementioned patents, a variable volume control device and an air diffuser can be combined in a single integrated assembly to provide an economical unit for controlling the distribution of conditioned air to a relatively large number of temperature control zones. Devices in which the duct pressure is used to supply operating power for the controls are commonly referred to in the industry as self-powered controlled diffusers.
In office buildings and other large facilities having a number of different zones for distribution of conditioned air, a relatively large number of control units must be installed and properly adjusted prior to occupancy of the building. Consequently, the amount of materials needed and the cost of labor required to install and initially adjust the controls represents a significant economic factor. Prior to installation, decisions are made as to which units are to be operated as stand alone units and which are to be operated in a master/slave relationship in groups controlled by common thermostats. Based on these decisions, the installation is carried out by arranging and connecting the different units in the appropriate fashion to function as intended. Later, after installation of the control units has been completed and the ceiling tiles or other building components are in place, it is necessary to operate the system and to make certain that it complies with engineering specifications. Typically, this is done by adjusting the control units to obtain the maximum air flow rate and comparing the measured maximum rate with the maximum design rate. After the system has been in operation for some time following occupancy of the building, it is not uncommon for changes to be made in the configuration or usage of the spaces which are served by the units. In this event, readjustments are required and it is sometimes even necessary for the units to be connected differently to best serve the new space arrangement.
In the past, attempts to minimize the field labor required for adjustment of the control units have involved either the preadjustment of the controls at the factory or the provision of a precalibrated dial on the control unit to facilitate adjustment in the field. Experience has shown that neither of these approaches has been successful in dealing with all of the problems noted above. If the controls are adjusted at the factory, it is necessary for each unit to be specially designated for a particular installation and at a particular place in that installation. This is undesirable because of the need to make detailed accountings as to which unit goes where and, perhaps even more importantly, because of the frequent occurrence of last minute changes necessitated by unforeseen circumstances. The use of a precalibrated dial on the control is equally unsatisfactory because many technicians are unwilling to accept that the flow rate is as specified unless they actually measure it to confirm that it is as specified.
Another drawback associated with all presently available self powered controlled diffusers is that access to their adjustment mechanisms is difficult at best. Some units require a cumbersome disassembly of a rather expensive apparatus and others have adjustment devices that are accessible only when access through the ceiling is provided. In ceilings having lift out ceiling tiles, access is possible without undue difficulty, but even then, a tall ladder is needed and the adjustment must be made in the dark area above the ceiling. If the ceiling is a more permanent structure, it is easy to appreciate that adjustment is much more difficult and usually impractical.
It is also beneficial in a number of respects for the diffuser mounted thermostat to be capable of being installed and removed from below the ceiling. This makes it easier to assure a wide open thermostat condition during adjustment of the high limit of the control. It is also makes inspection and replacement of the thermostat easier in the event that problems arise with a defective thermostat.
An ability to measure flow during adjustment is also important. Preferably, one should be able to make the measurement by attaching a gage to a measurement port accessible from below the ceiling.
Moreover, slave units can be converted to stand alone units easily at a later time when the building has been completed and is occupied.
The aforementioned U.S. Pat. Nos. 4,356,963 and 4,312,475 disclose cam operated adjustment dials used for adjustment of the maximum flow rate. The main problem with this type of adjustment mechanism is that the exhaust line can wobble and unpredictably change its height and angle of closure with the diaphragm. Access to the adjustment dial is also difficult from below the ceiling.